1. Field of the Invention
The present invention relates to a through anchor by which a webbing pulled out from a take-up device is folded and held in a slidable manner.
2. Description of the Related Art
As illustrated in FIG. 5, a three-point type seat belt apparatus 40 is used to safely hold a vehicle occupant in a seat S. One end of a webbing 42 of the seat belt apparatus 40 is taken up by a retractor 44 (take-up device) and another end thereof is fixed via a through anchor 46 to an anchor plate 50 supported at a lower end of a center pillar 48. Further, a tongue plate 52 provided in the webbing 42 between the anchor plate 50 and the through anchor 46 is engaged with a buckle 54 made upright substantially from the central portion of a vehicle body.
The through anchor 46 is used to fold the webbing 42 so as to fix, to the anchor plate 50, an end of the webbing 42 of which another end is taken up by the retractor 44. The through anchor 46 itself is also fixed to the center pillar 48, for example, by an adjuster mechanism which permits height control.
The through anchor 46 is structured as shown in FIG. 6. The through anchor 46 is manufactured by molding in which a metal plate 56 having an insertion hole 45 through which the webbing 42 is inserted to pass is set in a metal mold and resin is put into the metal mold. After the molding, a resin molding portion 58 covers a lower half section of the metal plate 56.
The resin molding portion 58 is formed by putting resin molten at a high temperature into the mold, and thereafter, cooled down. Accordingly, the resin forming portion 58 thermally contracts in the directions indicated by arrow B. In contrast, an insert portion 61 of the metal plate 56 does not typically thermally contract to a significant degree.
As a result, due to a difference in rate of shrinkage between the resin molding portion 58 and the insert portion 61 of the metal plate 56, residual stress is generated between the resin molding portion 58 and the metal plate 56. Particularly, a crack may form in a region A in the vicinity of each end of the resin molding portion 58 along a shoulder 57 of the metal plate 56.
Accordingly, in order to prevent occurrence of a crack, a high-strength material having a low rate of mold shrinkage is conventionally used as the resin molding portion 58 so as to prevent contraction of the resin molding portion 58 caused by residual stress. However, such high-strength materials are expensive.